boost program_options custom parsing - c++

Question

Is there a way to have something like
myapp hostname:port
parsed by boost program_options? I'm also using other options and I would love to use boost program_options without having to roll my own parser for argc/argv.
I tried with some combinations of
desc.add_options()
("help", "list all available options")
(new MyCustomValue(&store_var), "")
but it didn't work

Answer 1

As Dan Mašek writes, this looks more fitting for a positional argument. Since you specify a specific structure for the option, though, you might want to add std::regex_match.
Say you start with
#include <string>
#include <iostream>
#include <regex>
#include <boost/program_options.hpp>
using namespace std;
using namespace boost::program_options;
int main(int argc, const char *argv[]) {
try {
options_description desc{"Options"};
desc.add_options()
("help,h", "Help screen")
("ip_port", value<std::string>()->required(), "ip:port");
positional_options_description pos_desc;
pos_desc.add("ip_port", -1);
command_line_parser parser{argc, argv};
parser.options(desc).positional(pos_desc).allow_unregistered();
parsed_options parsed_options = parser.run();
variables_map vm;
store(parsed_options, vm);
notify(vm);
const auto ip_port = vm["ip_port"].as<string>();
At this point, we have the user's input for ip_port. We can define a regex to match it. Note that first part can be a string (e.g., localhost), but the second part must be an integer:
const regex ip_port_re("([^:]+):([[:digit:]]+)");
smatch ip_port_match;
if(!regex_match(ip_port, ip_port_match, ip_port_re))
throw validation_error{validation_error::invalid_option_value, ip_port, "ip_port"};
cout << "ip: " << ip_port_match[1] << " port: " << ip_port_match[2] << endl;
}
catch (const error &ex) {
cerr << ex.what() << '\n';
}
}
When running it, it looks like this:
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out 127.0.0.1:30
ip: 127.0.0.1 port: 30
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out localhost:30
ip: localhost port: 30
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out localhost:30d
the argument for option 'localhost:30d' is invalid
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out
the option '--ip_port' is required but missing
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out localhost:30 foo
option '--ip_port' cannot be specified more than once